Nematomorpha

{{Short description|Phylum of parasitoid animals; horsehair worms}} {{Automatic taxobox | fossil_range = {{fossil range|Cenomanian|Recent|earliest=Atdabanian}} Possible [[Atdabanian]] Record | image = Paragordius tricuspidatus.jpeg | image_caption = ''[[Paragordius tricuspidatus]]'' | display_parents = 7 | taxon = Nematomorpha | authority = [[František Vejdovsky|Vejdovsky]], 1886 | subdivision_ranks = Orders and families | subdivision = * [[Gordioidea]] Rauther, 1930 ** Chordodidae May, 1919 ** Gordiidae May, 1919 * [[Nectonematoidea]] Rauther, 1930 ** Nectonemidae Ward, 1892 | Clade = }}

'''Nematomorpha''' (sometimes called '''Gordiacea''', and commonly known as '''horsehair worms''', '''hairsnakes''',<ref>{{Cite web |url=http://stateoftheozarks.net/natural/snakes/horsehair.php |title=Horse Hair Snake |last=Heston |first=Joshua |website=State of the Ozarks |access-date=1 January 2021}}</ref><ref>{{Cite news |url=http://www.emmitsburgchronicles.com/wp-content/uploads/2018/10/EC_19030130.pdf |archive-url=https://web.archive.org/web/20210509081150/http://www.emmitsburgchronicles.com/wp-content/uploads/2018/10/EC_19030130.pdf |archive-date=2021-05-09 |url-status=live |last=Troxell |first=W.H. |title=Erroneous Beliefs |date=30 January 1903 |work=Emmitsburg Chronicle |issue=37 |access-date=1 January 2021}}</ref><ref>{{Cite web |url= http://imp.lss.wisc.edu/~jrvalent/BackUps/NLIP_Year_4_2008_bu13jul08/attachments/natconf.pdf |archive-url=https://web.archive.org/web/20201022213845/http://imp.lss.wisc.edu/~jrvalent/BackUps/NLIP_Year_4_2008_bu13jul08/attachments/natconf.pdf |archive-date=2020-10-22 |url-status=live |title=Naasaab Izhi-anishinaabebii'igeng conference report: a conference to find a common Anishinaabemowin writing system |last=Ningewance |first=Pat |date=8–10 August 1996 |publisher= Literacy Ontario |pages=27 |location=Toronto, Ontario |quote= Girls, don't swim without pants or a hairsnake will enter you.}}</ref> or '''Gordian worms''') are a [[phylum]] of [[parasitoid]] [[animal]]s similar to yet distinct from [[nematode]] [[worm]]s in [[morphology (biology)|morphology]], hence the name. Most species range in size from {{convert|5|to|10|cm|in|sigfig=1}}, reaching {{convert|2|m|ftin}} in extreme cases, and {{convert|1|to|3|mm}} in diameter. Horsehair worms can be discovered in damp areas, such as watering troughs, swimming pools, streams, puddles, and cisterns. The adult worms are free-living, but the [[larva]]e are [[parasite|parasitic]] on [[arthropod]]s, such as [[beetle]]s, [[cockroach]]es, [[mantises]], [[orthoptera]]ns, and [[crustacean]]s.<ref>{{Cite book |chapter=Biology of the phylum Nematomorpha |last1=Hanelt |first1=B. |first2=F. |last2=Thomas |first3=A. |last3=Schmidt-Rhaesa |title=[[Advances in Parasitology]] |volume=59 |year=2005 |pages=243–305 |doi=10.1016/S0065-308X(05)59004-3 |pmid=16182867 |isbn=9780120317592 }}</ref> About 351 freshwater species are known<ref name=Zhang2011>{{Cite journal| author=Zhang, Z.-Q.| title=Animal biodiversity: An introduction to higher-level classification and taxonomic richness | journal=Zootaxa| volume=3148| year=2011| pages=7–12| doi=10.11646/zootaxa.3148.1.3 | url=http://mapress.com/zootaxa/2011/f/zt03148p012.pdf |archive-url=https://ghostarchive.org/archive/20221010/http://mapress.com/zootaxa/2011/f/zt03148p012.pdf |archive-date=2022-10-10 |url-status=live}}</ref> and a conservative estimate suggests that there may be about 2000 freshwater species worldwide.<ref>{{Cite journal|title=Global diversity of hairworms (Nematomorpha: Gordiaceae) in freshwater|author=Poinar Jr., G|journal=Hydrobiologia|volume=595|issue=1|date=January 2008|pages=79–83|doi=10.1007/s10750-007-9112-3|bibcode=2008HyBio.595...79P |s2cid=37985613}}</ref> The name "Gordian" stems from the legendary [[Gordian knot]]. This relates to the fact that nematomorphs often coil themselves in tight balls that resemble knots.<ref>[[Ross Piper|Piper, Ross]] (2007), ''Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals'', [[Greenwood Press (publisher)|Greenwood Press]].</ref>

==Description and biology== Nematomorphs possess an external [[cuticle]] without [[cilia]]. Internally, they have only longitudinal muscle and a non-functional gut, with no [[excretory system|excretory]], [[respiratory system|respiratory]] or [[circulatory system]]s. The nervous system consists of a [[nerve ring]] near the anterior end of the animal and a [[ventral nerve cord]] running along the body.<ref name=IZ>{{Cite book |author= Barnes, Robert D. |year=1982 |title= Invertebrate Zoology |publisher= Holt-Saunders International |location= Philadelphia, PA|pages= 307–308|isbn= 978-0-03-056747-6}}</ref>

Reproductively, they have [[Dioecy|two distinct sexes]], with the internal fertilization of eggs that are then laid in gelatinous strings. Adults have cylindrical [[gonad]]s, opening into the [[cloaca]]. The larvae have rings of cuticular hooks and terminal stylets that are believed to be used to enter the hosts. Once inside the host, the larvae live inside the [[haemocoel]] and absorb nutrients directly through their skin. Development into the adult form takes weeks or months, and the larva [[ecdysis|moults]] several times as it grows in size.<ref name=IZ/> Depending on species, a mouth can be either absent or present in adults. Also the pharynx can be absent, cellular in structure or a cuticularized tube.<ref>[https://wisconsin.pressbooks.pub/animalparasitology/chapter/ben-hanelt/ Introduction to the Nematomorphs]</ref>

The adults are mostly free-living in freshwater or marine environments, and males and females aggregate into tight balls (''Gordian knots'') during mating.<ref name=manipulate/><ref>{{Cite journal|first=Andreas|last=Schmidt-Rhaesa|year=2002|title=Two Dimensions of Biodiversity Research Exemplified by Nematomorpha and Gastrotricha|journal=Integrative and Comparative Biology|volume=42|issue=3|pages=633–640|doi=10.1093/icb/42.3.633|pmid=21708759 |doi-access=free}}</ref>

[[Image:Spinochordodes in Meconema.jpg|thumb|left|''[[Spinochordodes tellinii]]'' and its ''[[Meconema]]'' host]] In ''[[Spinochordodes tellinii]]'' and ''[[Paragordius tricuspidatus]]'', which have [[grasshoppers]] and [[crickets]] as their hosts, the infection acts on the infected host's brain.<ref>{{cite journal|doi = 10.1016/S0020-7519(03)00014-6 |author = Thomas, F.|year=2003 |title=Biochemical and histological changes in the brain of the cricket ''Nemobius sylvestris'' infected by a manipulative parasite ''Paragordius tricuspudatus'' (Nematomorpha) |journal=[[International Journal for Parasitology]] |volume=33 |pages=435–443 |issue = 4| pmid=12705936 | url=https://hal.science/hal-00307180 |display-authors=etal}}</ref> This causes the host insect to seek water and drown itself, thus returning the nematomorph to water — according to Thomas ''et al.'', the "infected insects may first display an erratic behaviour which brings them sooner or later close to a stream and then a behavioural change that makes them enter the water", rather than seeking out water over long distances.<ref name=manipulate>{{Cite journal |last = Thomas |first = F. |author2 = Schmidt-Rhaesa, A. |author3 = Martin, G. |author4 = Manu, C. |author5 = Durand, P. |author6 = Renaud, F. |date = May 2002 |title = Do hairworms (Nematomorpha) manipulate the water seeking behaviour of their terrestrial hosts? |journal = [[Journal of Evolutionary Biology]] |volume = 15 |issue = 3 |pages = 356–361 |url = http://www.erin.utoronto.ca/~w3gwynne/BIO418/Nemato.pdf |doi = 10.1046/j.1420-9101.2002.00410.x |url-status = dead |archive-url = https://web.archive.org/web/20150924002153/http://www.erin.utoronto.ca/~w3gwynne/BIO418/Nemato.pdf |archive-date = 2015-09-24 |citeseerx = 10.1.1.485.9002 |s2cid = 86278524 }}</ref> ''Paragordius tricuspidatus'' is also remarkably able to survive the predation of their host, being able to wiggle out of the predator that has eaten the host.<ref>{{Cite journal|last = Ponton |first = Fleur |author2=Camille Lebarbenchon |author3=Thierry Lefèvre |author4=David G. Biron |author5=David Duneau |author6=David P. Hughes |author7=Frédéric Thomas |date=April 2006 |title = Parasitology: Parasite survives predation on its host |journal = [[Nature (journal)|Nature]] |pmid = 16598248 |volume = 440 |issue = 7085 |doi = 10.1038/440756a |page = 756 |bibcode = 2006Natur.440..756P |s2cid = 7777607 |url = https://hal.umontpellier.fr/hal-02992927/file/Ponton%20et%20al%202006%20nature.pdf }}</ref> Similarly, ''[[Chordodes]]'' sp. nematomorphs affect the light-interpreting organs of ''[[Hierodula patellifera]]'' mantises so the host is attracted to horizontally [[Polarization (waves)|polarized light]]. Thus the host goes into water and the parasite's lifecycle completes.<ref>{{Cite journal |last=Obayashi |first=Nasono |last2=Iwatani |first2=Yasushi |last3=Sakura |first3=Midori |last4=Tamotsu |first4=Satoshi |last5=Chiu |first5=Ming-Chung |last6=Sato |first6=Takuya |date=2021-06-21 |title=Enhanced polarotaxis can explain water-entry behaviour of mantids infected with nematomorph parasites |url=https://www.sciencedirect.com/science/article/pii/S0960982221006606 |journal=Current Biology |volume=31 |issue=12 |pages=R777–R778 |doi=10.1016/j.cub.2021.05.001 |issn=0960-9822}}</ref> Many of the genes the parasites use for manipulating their host have been acquired through [[horizontal gene transfer]] from the host genome.<ref>[https://www.popularmechanics.com/science/animals/a45575538/horsehair-worm-horizontal-gene-transfer/ This Parasitic Worm 'Steals' Genes From Its Unsuspecting Host]</ref>

There are a few cases of accidental parasitism in vertebrate hosts, including dogs,<ref>{{Cite journal |doi=10.3347/kjp.2015.53.6.719 |pmid=26797439|title=A Horsehair Worm, ''Gordius'' sp. (Nematomorpha: Gordiida), Passed in a Canine Feces |journal=The Korean Journal of Parasitology |volume=53 |issue=6 |pages=719–24 |year=2015 |last1=Hong |first1=Eui-Ju |last2=Sim |first2=Cheolho |last3=Chae |first3=Joon-Seok |last4=Kim |first4=Hyeon-Cheol |last5=Park |first5=Jinho |last6=Choi |first6=Kyoung-Seong |last7=Yu |first7=Do-Hyeon |last8=Yoo |first8=Jae-Gyu |last9=Park |first9=Bae-Keun |pmc=4725239}}</ref> cats,<ref>{{Cite journal |last1=Saito |first1=Y |last2=Inoue |first2=I |last3=Hayashi |first3=F |last4=Itagaki |first4=H |year=1987 |title=A hairworm, Gordius sp., vomited by a domestic cat |journal=Nihon Juigaku Zasshi. The Japanese Journal of Veterinary Science |volume=49 |issue=6 |pages=1035–7 |doi=10.1292/jvms1939.49.1035 |pmid=3430914 |doi-access=free}}</ref> and humans. Several cases involving ''Parachordodes'', ''Paragordius'', or ''Gordius'' have been recorded in human hosts in Japan.<ref>{{Cite journal|doi=10.3347/kjp.2012.50.3.263|pmid=22949758|title=Two Human Cases Infected by the Horsehair Worm, Parachordodes sp. (Nematomorpha: Chordodidae), in Japan |journal=The Korean Journal of Parasitology |volume=50 |issue=3 |pages=263–7 |year=2012 |last1=Yamada |first1=Minoru |last2=Tegoshi |first2=Tatsuya |last3=Abe |first3=Niichiro |last4=Urabe |first4=Misako|pmc=3428576}}</ref>

== Life cycle and development == The Nematomorpha life cycle consists of four stages: (1) the [[egg]], (2) the pre-parasitic [[larva]], (3) the parasitic larva, and (4) the free-living aquatic adult.<ref name=":0">{{Cite journal |last=Kaya |first=H. K. |date=March 2013 |title=Horsehair Worms: Integrated Pest Management around the Home |url=https://ipm.ucanr.edu/legacy_assets/PDF/PESTNOTES/pnhorsehairworms.pdf |journal=UC Statewide Integrated Pest Management Program |volume=Publication 7471}}</ref> Throughout these four stages, the worms parasitize multiple [[invertebrate]] hosts, inhabiting different environments.<ref name=":0" />

Freshwater worms typically mate in the spring, depositing their strings of eggs in the water.<ref name=":0" /> Within 3 to 4 weeks, pre-parasitic larvae emerge from these eggs.<ref name=":0" /> These larvae must parasitize an invertebrate host — their primary hosts being larger [[arthropod]] species, such as [[Mantidae|mantids]], [[Beetle|beetles]], [[Dragonfly|dragonflies]], [[Cricket (insect)|crickets]], and [[Grasshopper|grasshoppers]].<ref name=":0" /><ref name=":1">{{Cite journal |last=Schmidt-Rhaesa |first=Andreas |last2=Ehrmann |first2=Reinhard |date=2001 |title=Horsehair Worms (Nematomorpha) as Parasites of Praying Mantids with a Discussion of their Life Cycle |url=https://linkinghub.elsevier.com/retrieve/pii/S0044523104700133 |journal=Zoologischer Anzeiger - A Journal of Comparative Zoology |language=en |volume=240 |issue=2 |pages=167–179 |doi=10.1078/0044-5231-00014|url-access=subscription }}</ref> Some studies report that mantids are among the most important primary hosts of Nematomorpha in [[Tropics|tropical]] and [[Subtropics|subtropical]] regions.<ref name=":1" />

The Nematomorpha life cycle often includes multiple hosts.<ref name=":1" /> If aquatic larvae are fortunate enough to be ingested by a primary host organism, they will then continue their development into adults.<ref name=":0" /> However, it is much more common that they seek out an intermediate host, usually aquatic invertebrate [[Larva|larvae]] (e.g. [[mayfly]] larvae, [[mosquito]] larvae, or [[Chironomidae|chironomid]] larvae).<ref name=":0" /><ref name=":1" /> Once larvae find themselves in an intermediate host, they encyst themselves in the host's [[body cavity]].<ref name=":0" /><ref name=":1" /> These parasites leverage aquatic insects as vehicles to move from water to land, retaining viable [[Cyst|cysts]] through [[metamorphosis]].<ref>{{Cite journal |last=Hanelt |first=B. |last2=Janovy |first2=J. |date=2004 |title=LIFE CYCLE AND PARATENESIS OF AMERICAN GORDIIDS (NEMATOMORPHA: GORDIIDA) |url=http://www.bioone.org/doi/abs/10.1645/GE-78R |journal=Journal of Parasitology |language=en |volume=90 |issue=2 |pages=240–244 |doi=10.1645/GE-78R |issn=0022-3395|url-access=subscription }}</ref> Once conditions to continue development are met (i.e. the intermediate host is eaten by a primary host), they will reemerge from this cyst and infect the primary host.<ref name=":0" /><ref name=":1" />

Some pre-parasitic freshwater Nematomorpha larvae are known to encyst themselves on debris or vegetation.<ref name=":0" /> If they are ingested by a primary host organism (such as a [[millipede]]) in this state, they will then progress into the parasitic stage.<ref name=":0" />

== Community ecology == [[File:Habitus saitenwurm zarbach benecke.jpg|thumb|Mermithid worm (Phylum Nematoda), often confused with horsehair worms (Phylum Nematomorpha). Dark structures are eggs, not seen in horsehair worms. Germany 2021. ]]Owing to their use of [[orthoptera]]ns as hosts, nematomorphs can be significant factors in shaping community ecology. One study conducted in a Japanese [[riparian]] ecosystem showed that nematomorphs could cause orthopterans to become 20 times more likely to enter water than uninfected orthopterans; these orthopterans constituted up to 60% of the annual energy intake for the [[Kirikuchi char]]. The absence of nematomorphs from riparian communities can thus lead to char preying more heavily on other aquatic invertebrates, potentially causing more widespread physiological effects.<ref>{{Cite journal|last1=Sato|first1=Takuya|last2=Watanabe|first2=Katsutoshi|last3=Kanaiwa|first3=Minoru|last4=Niizuma|first4=Yasuaki|last5=Harada|first5=Yasushi|last6=Lafferty|first6=Kevin D.|date=2011|title=Nematomorph parasites drive energy flow through a riparian ecosystem|journal=Ecology|language=en|volume=92|issue=1|pages=201–207|doi=10.1890/09-1565.1|pmid=21560690|bibcode=2011Ecol...92..201S |issn=1939-9170|hdl=2433/139443|s2cid=20274754 |hdl-access=free}}</ref>

==Taxonomy== {{See also|List of bilaterial animal orders}} Nematomorphs can be confused with nematodes, particularly [[Mermithidae|mermithid]] worms. Unlike nematomorphs, mermithids do not have a terminal cloaca. Male mermithids have one or two spicules just before the end, apart from having a thinner, smoother cuticle without areoles and paler brown colour.<ref>{{Cite web |first1=Malcolm S. |last1=Bryant |first2=Robert D. |last2=Adlard |first3=Lester R.G. |last3=Cannon |year=2006 |title=Gordian Worms: Factsheet |website=[[Queensland Museum]] |url=http://www.qm.qld.gov.au/inquiry/factsheets/Gordian_Worms_20070605.pdf |access-date=2008-03-10 |url-status=dead |archive-url=https://web.archive.org/web/20080722175823/http://www.qm.qld.gov.au/inquiry/factsheets/Gordian_Worms_20070605.pdf |archive-date=2008-07-22 }}</ref>

The phylum is placed along with the [[Ecdysozoa]] clade of moulting organisms that include the [[Arthropod]]a. Their closest relatives are the nematodes. The two phyla make up the group [[Nematoida]] in the clade [[Cycloneuralia]]. During the larval stage, the animals show a resemblance to adult [[kinorhyncha]] and some species of [[Loricifera]] and [[Priapulida]], all members of the group [[Scalidophora]].<ref>[http://www.bumblebee.org/invertebrates/NEMATOMORPHA.htm Nematomorpha – Bumblebees]</ref> The earliest nematomorph could be ''[[Maotianshania]]'', from the Lower Cambrian; this organism is, however, very different from extant species;<ref>{{Cite journal|last1= Sun|first1= W.|last2= Hou|first2= X.|year= 1987|title= Early Cambrian worms from Chengjiang, Yunnan, China: ''Maotianshania'' gen. nov.|journal= Acta Palaeontologica Sinica|volume= 26|issue= 3|pages= 299–305|url= http://en.cnki.com.cn/Article_en/CJFDTOTAL-GSWX198703007.htm|format= Paywall|archive-date= 2023-01-23|access-date= 2014-10-13|archive-url= https://web.archive.org/web/20230123211404/http://en.cnki.com.cn/Article_en/CJFDTOTAL-GSWX198703007.htm|url-status= dead}}</ref> fossilized worms resembling the modern forms have been reported from mid [[Cretaceous]] [[Burmese amber]] dated to 100 million years ago.<ref>{{Cite journal |author1=Poinar George |author2=Ron Buckley | date = September 2006 | title = Nematode (Nematoda: Mermithidae) and hairworm (Nematomorpha: Chordodidae) parasites in Early Cretaceous amber | journal = [[Journal of Invertebrate Pathology]] | volume = 93 | issue = 1| pages = 36–41 | doi = 10.1016/j.jip.2006.04.006 | pmid = 16737709 |bibcode=2006JInvP..93...36P }}</ref>

Relationships within the phylum are still somewhat unclear, but two classes are recognised. The five marine species of nematomorph are contained in [[Nectonematoida]].<ref name="PechenikTaxo">Pechenik, '''Biology of the Invertebrates'', 2010, pg 457.</ref> This order is monotypic containing the genus ''[[Nectonema]]'' Verrill, 1879: adults are planktonic and the larvae parasitise [[Decapoda|decapod crustaceans]], especially crabs.<ref name="PechenikTaxo"/> They are characterized by a double row of natotory [[seta]]e along each side of the body, dorsal and ventral longitudinal epidermal cords, a spacious and fluid-filled [[blastocoelom]] and singular [[gonad]]s.

The approximately 320 remaining species are distributed between two families,<ref name="itisGodioidea">{{ITIS|id=699878 |taxon=Gordioidea}}</ref> within the monotypic class [[Gordioida]]. Gordioidean adults are free-living in freshwater or semiterrestrial habitats and larvae parasitise insects, primarily [[orthoptera]]ns.<ref name="PechenikTaxo"/> Unlike nectonematiodeans, gordioideans lack lateral rows of setae, have a single, ventral epidermal cord and their blastocoels are filled with [[mesenchyme]] in young animals but become spacious in older individuals.

==References== === Citations === {{Reflist}}

=== General and cited references === * {{Cite book|last=Pechenik|first=Jan A.|title=Biology of the Invertebrates|edition=6th International|year=2010|publisher=Mc-Graw Hill Education (Asia)|location=Singapore|isbn=978-0-07-127041-0|pages=452–457|chapter=Four Phyla of Likely Nematode Relatives}}

== Further reading == * {{Cite journal |vauthors=Baker GL, Capinera JL |year=1997 |title=Nematodes and nematomorphs as control agents of grasshoppers and locusts |journal=Memoirs of the Entomological Society of Canada |volume=171 |pages=157–211 |doi=10.4039/entm129171157-1}} * {{Cite book |chapter=Biology of the phylum Nematomorpha |last1=Hanelt |first1=B. |first2=F. |last2=Thomas |first3=A. |last3=Schmidt-Rhaesa |title=[[Advances in Parasitology]] |volume=59 |year=2005 |pages=243–305 |doi=10.1016/S0065-308X(05)59004-3 |pmid=16182867 |isbn=9780120317592 }} * {{Cite book |author=Poinar GO Jr |year=1991 |chapter=Nematoda and Nematomorpha |pages=249–283 |veditors=Thorp JH, Covich AP |title=Ecology and Classification of North American Freshwater Invertebrates |publisher=Academic Press |location=San Diego, CA}} * {{Cite journal |author=Thorne G |year=1940 |title=The hairworm, ''Gordius robustus'' Leidy, as a parasite of the Mormon cricket, ''Anabrus simplex'' Haldeman |journal=Journal of the Washington Academy of Sciences |volume=30 |pages=219–231}}

==External links== {{EB1911 poster|Nematomorpha}} * Capinera, J. L. [http://edis.ifas.ufl.edu/in274 Horsehair Worms, Hairworms, Gordian Worms, Nematomorphs, ''Gordius'' spp. (Nematomorpha: Gordioidea).] University of Florida [[Institute of Food and Agricultural Sciences|IFAS]]. Published 1999, revised 2005. * [https://www.youtube.com/watch?v=76BnVsaLiR0 Nematomorph worm – Behavior modification of cricket by nematomorph worm.] YouTube. * Gordian worms discussed on [[Radio New Zealand|RNZ]] ''[[Critter of the Week]]'', [http://www.radionz.co.nz/national/programmes/afternoons/audio/201777689/critter-of-the-week 6 November 2015]

[[Category:Nematomorpha| ]] [[Category:Ecdysozoa phyla]] [[Category:Nematoida]] [[Category:Parasitic protostomes]] [[Category:Suicide-inducing parasitism]]